Some things you may not have known about Sloths
by María Pía Martín, DVM
The sloths are part of the Xenartha order which also includes anteaters and armadillos. This bizarre order is only found in Central and South America. They are different from all other animals in that they have an unusual lower back vertebrae and two vena cava (returns blood to the heart, the other mammals have only one).
Evolution
They are some of the most ancient mammals and have been on Earth for more than 60 million years ago. For example, they are so primitive that their reproductive and digestive tract open into a single chamber called cloaca, like birds and reptiles.
At the beginning, the Megatherium were 6 meters (20 feet) tall giant ground sloths.
Body
Sloths are mostly folivores (leaf-eaters). They have ten teeth on the upper jaw and eight on the lower jaw.
Sloths break down cellulose through a process of bacterial fermentation like deer, cows, howler monkeys, and manatees. A leaf diet poses another problem for sloths, such as low energy, and this requires a very large stomach (almost a third of body weight), yet sloths must stay light enough to move along tree branches without breaking them.
Sloths have another peculiar skeletal feature. While almost all other mammals consistently have seven neck vertebrae, two toed sloths have six to eight and three toed sloths have eight or nine. So sloths are able to rotate their heads an impressive 180°.
They have unusually low body temperatures and metabolic rates (24-33°C or 77-96°F) which burn less energy.
With their laziness they can spend up to 20 hours motionless, and most of it sleeping. Some scientists believe that by moving so slowly they avoid their biggest predators (eagle and jaguar).
Their hair is unique. It has corrugations and cracks that encourage the growth of algae and through a symbiotic relationship, the algae gains shelter and the sloth camouflage.
Senses
Their sense of sight and hearing is poor and it seems that their most effective is smell.
Behavior
They are middle size mammals, strictly arboreal, and spend most of their time hanging from the branches of trees; they even sleep, give birth and carry their young like this.
They are very clumsy on land but are great swimmers.
Sloths defecate once a week and this is the only time they come down to the floor.
The two species found in Costa Rica are the two toed and three toed sloth, but don’t let the name fool you, all sloths have three toes! The difference is in the fingers of their hands!
Three toed sloths have a mask in their face, are grayish in color with a black stripe in their back, while two toed sloths have a lighter brown and uniform color.